Cutter type excavator machines are usually used for making trenches in the ground to considerable depth, up to 100 meters (m), and of width that is relatively small compared with said depth, the width typically lying in the range 500 millimeters (mm) to 1500 mm. One of the advantages of such machines is to enable such deep trenches to be made while complying with a requirement for being rigorously vertical. The trench of the hole is obtained by successively digging adjacent panels.
In general, cutters are constituted by a box structure of considerable height that serves to provide mechanical guidance to the excavator machine as the trench is being made. At the bottom end of the box structure there is a cutter head. These machines are themselves well known and it therefore suffices to mention that the cutter head is usually constituted by two cutter motors each usually carrying a pair of drums on which cutter tools are mounted. Each pair of drums rotates about a common axis, with the two axes of the cutter motors being parallel and horizontal in use. The cutter drums are driven in rotation by hydraulic motors.
Various types of mount are possible. In the configuration adopted in particular by the supplier Bauer, the hydraulic motor is placed inside the box structure above the cutter head. It transmits power via a substantially vertical shaft of small diameter that passes within the thickness of the plate that forms the bearing of the cutter motor. The vertical shaft engages a pair of bevel gears that deliver motion to the horizontal shaft. An epicyclic gear system reduces the speed of rotation and increases torque so as to provide the cutter drums with effective drive.
In another configuration, made available in particular by the supplier Casagrande, the hydraulic motors are located in the bottom portion of the box structure of the machine above the cutter head, and power is transmitted to the cutter drum by a transmission chain.
European patent EP 0 262 050 in the name of Soletanche, discloses a method of driving cutter drums in which the single hydraulic motor is mounted inside the cutter drums and is connected thereto by a stage of reduction gearing, or else by direct transmission. The way in which hydraulic power is applied to the motor is not described.
The first two types of excavator machine mentioned above present the major drawback of having hydraulic motors above the cutter head and thus of mounting those motors in a manner that is more complex and more expensive. In particular, it is not possible to change the cutter heads quickly.
Furthermore, the elements of the drive transmission system for the first two types of cutter (gearing, speed reduction, chain) leads to relatively high losses, of the order of 15%, that do not occur in the configuration described in the European patent in the name of Soletanche.
It should be added that depending on the nature of the work and the terrain being excavated, it can be advantageous to be able to vary the parameters relating to speed of rotation and torque for the cutter drums.
The thickness of the cutter head is determined by the width of the trench to be made and may lie in the range 500 mm to 1500 mm. The present invention relates to an excavator machine of small width, typically lying in the range 500 mm to 800 mm.
It will be understood, that with such small thickness, special problems can arise in providing the means for driving the drum.